1 Large or 2 small?

[bopster]

All 3 ovens are together in a line of tall housings along with a warming drawer.
The ovens pull nearly 4kw each and warranty states dedicated circuit.
Yes having a 6 burner gas hob

 

[ericmark]

The arguement for 2 boards is good as loading has the potential to overload main switch.

No maximum rating for DNO fuse is 100A. To exceed that one would need a set of fuses to split into circuits. I have done it with one massive house we fitted three consumer units and wired to a fuse box and isolator with a 80A fuse to each consumer unit. The fuse box rated 160A three phase so we could configure for three, split or single phase at up to 160A per phase but this is unusual.

In hind sight it was not required. The 100A supply fuse never ruptured and it could have been feed with one large consumer unit.

I will not say all as likely there is some odd one out but all consumer units I have seen are rated 100A so that is maximum size of DNO fuse. There are larger distribution units but for a house under the control of an ordinary person a type tested distribution unit is required which is called a consumer unit.

In hind sight not sure if the DNO should have connected the supply to our fused isolator as it was not considered as type tested. Clearly it was a standard unit but at the time I was more commercial and had not realised I needed to use type tested equipment in domestic.

 

[JohnW2]

... all consumer units I have seen are rated 100A so that is maximum size of DNO fuse. There are larger distribution units but for a house under the control of an ordinary person a type tested distribution unit is required which is called a consumer unit. ... Clearly it was a standard unit but at the time I was more commercial and had not realised I needed to use type tested equipment in domestic.

All the regs actually say is that, for a single-phase supply up to 100A under the control of ordinary persons, switchgear and control gear assemblies should EITHER comply with BS EN 60439-3 OR be a (type tested') consumer unit, the components and protective devices of which comply with BS EN 60439-3.

I don't know what BS EN 60439-3 says/requires, but it would seem that there is no compulsion to use a type-tested CU in domestic situations - that is just one of the options specified. Furthermore, as written, the regulation in question (530.3.4) would not even apply if one had a supply >100A.

Kind Regards, John

 

[JohnW2]

All 3 ovens are together in a line of tall housings along with a warming drawer. The ovens pull nearly 4kw each and warranty states dedicated circuit.

I suspect that opinions about this (and about the definition of "a dedicated circuit" {'dedicated' to one oven, or to three ovens?} ) will vary but 12kW worth of ovens only represents an after-diversity load of about 22A, hence easily supplied by one 32A circuit.

Kind Regards, John

 

[bopster]

For the sake of the additional circuits they may as have separate circuits, ovens cost 700+ each so whats the point faffy around if warranty is called upon.

 

[JohnW2]

For the sake of the additional circuits they may as have separate circuits, ovens cost 700+ each so whats the point faffy around if warranty is called upon.

Fair enough - that's obviously your choice/decision, and there's nothing electrically wrong with what you propose.

However, I think that, although they are going to be 20A circuits, you should seriously consider using cable for at least one or two of them large enough to support a 32A MCB - in case someone (maybe even you) decides that they want/need a more conventional cooker supply circuit at some point in the future.

Kind Regards, John

 

[bopster]

ovens are going to be in 6mm for that very reason, apart from i have a 100m drum of the stuff that a customer gave me as i present

 

[JohnW2]

ovens are going to be in 6mm for that very reason, apart from i have a 100m drum of the stuff that a customer gave me as i present

Fair enough!

Another approach, I suppose, would be to have just one 6mm² feed from the main CU (on a 32A or 40A MCB) and then to have a mini CU/enclosure hidden somewhere in the kitchen with 3 x 20A MCBs, just to keep the ovens' warranties happy!

Kind Regards, John

 

[bopster]

That would work but due to the CU being directly above the ovens I'll just have all 3 direct to there mcbs

 

[ban-all-sheds]

You may well be competent to do the work - I obviously having no way of knowing. However, as has been said, even if competent, you would not be able to self-certify a CU change unless you had full scope membership of a self-certification scheme.

We don't know that he is self-certifying through his scheme membership (I thought that they'd all dropped the defined/full-scope idea though?).

The extension will have been notified, so the electrical work probably doesn't need self-certification.

 

[JohnW2]

That would work but due to the CU being directly above the ovens I'll just have all 3 direct to there mcbs

Again, fair enough. All of this discussion has only really about possible ways of reducing the number of ways needed in your CU(s)!

Kind Regards, John

 

[JohnW2]

We don't know that he is self-certifying through his scheme membership ...

That's true, which is why I asked the question ...

Are you a member of a self-certification scheme which would enable you to self-certify a CU change?

Yes I can self certify it ...

However...

The extension will have been notified, so the electrical work probably doesn't need self-certification.

Maybe, but would not the (electrical) scope of that notification be restricted to work related directly to the (notified) extension, not replacement of a house-wide CU?

Kind Regards, John

 

[ban-all-sheds]

All of this discussion has only really about possible ways of reducing the number of ways needed in your CU(s)!

Naah

 

[ban-all-sheds]

Maybe, but would not the (electrical) scope of that notification be restricted to work related directly to the (notified) extension, not replacement of a house-wide CU?

Depends how the work was described. If the extension means extra circuits and a larger CU is needed, then...

 

[JohnW2]

Depends how the work was described. If the extension means extra circuits and a larger CU is needed, then...

As you say, it depends upon what was described. However, it looks to me as if the OP's proposals may well include new circuits which are nothing to do with the extension, and I would not have thought it very likely that such things would have been described in a notification relating to the extension. However, only he can tell us that.

Kind Regards, John